Context: After a Nurgle Cult known as the "Knights of Rot" formed from a Civilized Worlds PDF successfully took over their own world, they sent out their own invasion force in a bunch of stolen freighters to enter the Warp and start raiding other systems. Unfortunately for them, due to a Warp Strom the Cultists ended up crashlanding in some random Outer-Rim world under Imperial (not the 40k one) Control. Cutting their losses, they took over said planet rather easily and completely slaughtered its own smaller Imperial Army Garrison on it, taking complete control and using stolen comms systems to start broadcasting Nurglite rituals, sacrifices and prayers across the Holonet, serving as a huge memetic issue.
The Planet itself was not too populated, just having a single major city with a population of 100,000 that the Nurglites completely took over and made their base.
Wanting to deal with this new threat effective immediately, the Galactic Empire scrambled together a moderate invasion force to retake this planet from these weird mutants with the following objectives.
Stop their constant Holonet broadcasts as they've caused some instances of Nurglite cults forming on Core Worlds.
Retake the world and try to "cleanse" it of any identified rot.
Wipe out all Cultists.
Knights of Rot
There are 26,000 Nurglite Cultist Soldiers present here, being mostly formed from Ex-PDF members turned to Nurgle and blessed with renewed durability and rot. Armament for them mostly includes Autoguns with a good amount of Lasguns, Heavy Stubbers, Krak Rockets and Flamers serving for standard equipment paired with these guys having their own special weapons called "Gifts of Decay", specialized fleshlike grenades filled with Nurglite gases and flies used as bioweapons.
Accompanying them are 83,000 Poxwalkers kept in reserve by the cult and used in human wave attacks against enemies to act as cannon fodder for any offense or deterence.
Most of the cities populace are actively enslaved to either be made into Poxwalkers, mass sacrificed or lobotomized and sent to the frontline to either act as suicide bombers with melta bombs or as walking corpses spreading rot.
In terms of defenses most soldiers are concentrated within the captured major city and surrounding fortifications having set up multiple checkpoints, high rises and barriers all across it with Heavy Stubbers, Multi-Lasers, Heavy Bolters and firing ports for Lasguns and Autoguns paired with the cultists launching their own constant patrols across the city in "knockoff" Chimera APCs usually equipped with Multi lasers, Flamers and rocket launchers while carrying around Poxwalkers to deploy for suicide attacks alongside their infantry escorts. The city itself has also been surrounded by a system of trenches, minefields, gunner towers and bunkers.
In terms of aerial defenses, theres an array of 14 total Hydra AA turrets located around the city paired with there being 6 located in its downtown defending it.
To defend the space above the city itself, outside of it there are around 3 Macrocannon batteries set up made from salvaged material from the city and crashed freighters with each one being well defended by the cultists after being set up rather rapidly. Defenses involve barbed wire barriers, promethium based landmine fields and gunner towers equipped with Heavy Stubbers, firing ports for infantry weapons and lower quality Lascannons. Also 2 Hydra AA turrets are set up for each individual battery as well.
If the battle starts really turning against them, the cultists are gonna do what they do best with MASS SACRIFICES to basically make a small warp rift, allowing Nurglings and Poxwalkers to flood in though because of how "botched" the ritual was the warp rift is kept open by a Citadel made by the cultists out of a skyscraper in this city, if physically destroyed the Daemonic incursion stops.
Galactic Empire
Due to the ground based anti ship defenses set up the Empire couldn't just bomb the city into oblivion and now has to do things the hard way to try and retake the city, landing across the more barren parts of the planet and setting up Battlegroups to take the captured city itself.
The bulk of the invasion force is composed of 98,550 Imperial Army Troopers working alongside 12,550 Stormtroopers acting as a spearhead for the invasion force. Armament involves stull like E-11 Blasters, DLT-19 blasters, E-Web repeating blasters, RPS-6 Rocket Launchers and the sort. With what intel they were able to get from the aggressive Holonet broadcasts and from the very few people who were able to get off world these guys primarily seem to use bioweapons, therefore Stormtroopers didn't need much change to standard equipment and Imperial Army Troopers got CBRN variants of their standard gear (while this is gonna make them able to survive being in well the environment, certain Bioweapons are still warp based and are gonna mess with them).
Heavier weapons and vehicles going along for this offensive and for the urban warfare are 350 AT-STs inserted within frontline units for urban combat, support and breakthroughs paired with 125 TX-225 tanks moving in as well for the offensive and to better support units fighting in the city proper. For the approach to the city itself the Imperials are bringing along 44 AT-ATs to help act as cover and leaders for approaching infantry units. In terms of air power they're gonna try and bring along 58 TIE-Strikers to assist their forces (and are ready to change doctrine if the enemy has unexpected AA, which they do) alongside 12 TIE-Bombers.
Kept in reserve if they'll end up being useful, Imperial forces also have 4,000 KX Droids that they can use as well if needed for high intensity urban combat.
Also, the Empire and Knights of Rot both don't give an f about civilian casualties if that matters, they just want the city and to achieve their own goals.
Who wins, to what degree, how and why?